The present invention relates to remote telephone systems in which a remote unit transmits outgoing telephone signals from a microphone to a network associated receiver for transmission over the telephone network and receives incoming messages from the telephone network for application to a loudspeaker from which incoming messages are broadcast to the user at the remote unit. In such systems the distance between the remote unit and the network associated system can vary significantly. This variation will affect the perceived level of the signal broadcast on the loudspeaker. In addition, variations in telephone network line characteristics can change the signal level and noise on the incoming message received for broadcast by the loudspeaker.
In order to adapt the signal level of messages applied to the network some form of automatic attenuation or gain control is typically utilized to attenuate the signal received from the remote unit so that when it is applied to the network it will not exceed a predetermined signal level and is generally maintained at that level. Circumstances can exist where the received signal level is insufficient to maintain that level and permit application of a signal of desired strength to the network, for example, if the microphone on the remote unit is held at too great a distance from the user's mouth or the user speaks too soft. Some means is therefore desirable to prevent this circumstance.
Because, as noted above, the perceived signal level of the audio broadcast from the loudspeaker to the user at the remote location can vary, some form of volume control over this broadcast level is desirable to maintain a predetermined loudness or preceived loudness at the location of the remote unit. Such a volume control, however, must be under the control of the user at the remote unit in order to be practical. The capability of providing remote volume control does not exist or would exist only through the additional complexity of the transmission from the remote unit of an additional control signal.